a. Field of the Invention
The present invention relates generally to coil spring drives or motors, which are useful in numerous applications and, in particular, to the application of such coil spring drives in window cover systems.
b. Definitions and Applicability
Typically, as used here, "cover" refers to expandable or extendible structures. These include slat structures such as so-called venetian or slat blinds and so-called mini-blinds. These structures also include pleated folding structures such as single and plural pleat structures and box, hollow and cellular structures. "Cover" also refers to flat, sheet-type covers such as roller blinds. In this document, "cover" and "blind" are frequently used interchangeably. As applied to such covers, "operate" refers to the process of closing and opening the covers, typically (for horizontal covers) to lowering and raising the cover.
As used here, "horizontal" window cover refers to horizontally oriented covers such as horizontal slat blinds, horizontal folded pleat blinds and horizontal cellular blinds. The present invention is applicable generally to horizontal window cover systems and to flat window cover systems. It is understood that "window," as used for example in "window cover," includes windows, doorways, openings in general and even non-opening areas or regions to which "window" covers are applied for decoration, display, etc.
c. Current State of the Relevant Field
Typically a horizontal cover or blind is mounted above a window or space which is to be covered, and is operated using lift cords to extend the cover and lower it across the area, stopping at a selected position at which the blind partially or fully covers the area. For typical horizontal slat blinds, the lift cords are attached to a bottom rail and the individual slats are supported by the cross members or "rungs" of a separate cord ladder. When the blind is fully lowered, each slat is supported by a rung of the cord ladder and relatively little weight is supported by the lift cords. However, as the blind is raised, the slats are "collected" on the bottom rail, and the support of the slats is thus increasingly transferred from the cord ladder to the bottom rail and the weight supported by the rail and the lift cords increases.
Typical pleated, cellular, box, etc., blinds are formed of resilient material having inherent spring-like characteristics. As the resilient blind is raised toward the fully open position, the blind material is increasingly compressed, and requires increasingly greater force to overcome the compression force and move the blind and hold the blind in position. Effectively, then, both the slat blind and the pleated blind require increasingly greater force to open the blind and to maintain the blind open than is required to close the blind and maintain the blind closed.
So-called coil spring drives have operating characteristics which make it difficult to assist the opening and closing operation of blinds such as horizontal and flat blinds. As applied to downward-closing embodiments of such blinds, coil spring drives typically are mounted at the top of the blind, and are operatively connected or coupled to the shaft about which the blind lift cord is wound. As described above, as the blind is lowered, the slat weight supported by the lift cords decreases and the compression force of the pleats decreases. However, as the blind is lowered, the spring is wound and the energy stored in the spring increases, such that the increasing torque or force of the spring may then raise the blind in fast, uncontrolled fashion. Also, it may be difficult to keep the blind at a selected position. Furthermore, if the blind is heavy, and requires a strong spring to maintain the blind open, the blind is particularly susceptible to instability and uncontrolled raising operation when partially or fully extended or closed. Conversely, when the blind is at or near the upper limit of its travel (i.e., is open), the slat weight supported by the lift cords and the pleat compression is at or near maximum, while the spring torque is at or near minimum. In this position, then, unless the spring is strong (perhaps causing uncontrolled operation), the spring torque may be insufficient to keep the blind open.
Frequently, prior art coil spring drives use latching mechanisms in an attempt to hold the blind or cover in position.